AN ELECTROMYOGRAPHIC STUDY OF THE INTRAMUSCULAR EFFECTS OF THE CHIROPRACTIC ADJUSTMENT: A Pilot Study

There have been many attempts to record changes in the activity of the superficial spinal musculature following manipulative therapy by means of Electromyography (EMG). However, the question asked in this study was "By utilising bipolar intramuscular electrodes (BIM) can an association between intrinsic muscle action potentials and the chiropractic subluxation be demonstrated?" The rotatorae muscles are the deepest of the intrinsic muscle groups and are intimately associated with the intrinsic movements of the thoracic motion segment. The areas chosen for this study included segments from T1 to T4 as the rotatorae muscles at these levels are the most developed. All EMG activity was monitored using a Medelec MS6 mainframe recording unit. The BIM electrodes were paired, 71mm diameter polyurethane coated copper wires, threaded through a 41 mm length of 27 gauge dental needle and bent back to achieve an interelectrode distance of 2mm. This was then inserted to the desired depth of 4cm and then withdrawn to leave the BIM electrodes imbedded in the rotatorae muscle. Control electrodes were placed 4 spinal segments lower than the experimental level on the homolateral side of experimental spinal segment. It was found that the fixated segment's rotatorae muscles has an EMG background reading at rest. It was postulated that this facilitated state of the muscle was generated at the neuromere as a result of aberrant afferent input from the associated general somatic afferents directly innervating that spinal segment. A decrease in amplitude and frequency of the action potential was observed in the rotatorae muscles, after spinal adjustment. Control readings were taken to assess the change in EMG activity associated with habituation to the experimental procedure with time. It was found that there was no change in the action potential that could be attributable to habituation. This pilot study suggests a potentially effective way of analysing the effects of spinal manipulative therapy on the intrinsic muscles of the spine. Preliminary data indicated an increase in action potential, of the rotatorae muscles associated with a national chiropractic subluxation, and de-facilitation of those muscles following a chiropractic adjustment.